Pumps for pumping molten metal of the type that include a motor driven impeller typically position the impeller on the end of a shaft inside an impeller chamber of an elongated base having an inlet and outlet from the impeller chamber. Upon rotation of the impeller, molten metal is drawn into the base into the impeller chamber and then travels to the outlet of the base. If the pump is a circulation or submerged discharge pump, the outlet of the base extends as a passageway to the outer surface of the base, which circulates the molten metal through a furnace or hearth, for example. If the pump is a transfer pump, the outlet can lead to a riser spaced apart from the shaft, which extends above the pump to a conduit which directs the molten metal to another location such as to a ladle or to a die casting machine. All of the components of the pump that are in the molten metal environment are typically made of refractory material such as graphite, ceramic, graphite with a ceramic covering or graphite impregnated with a refractory oxide.
Flux is typically added to molten metal circulating through the hearth or furnace by injecting the flux along with a gas stream through a lance operated by hand. The flux is used to clean the molten metal, for example, and is typically in particulate form. This process is cumbersome and hazardous to workers who have to be near the molten metal when operating the lance. Attempts to replace the hand lancing of flux addition by designing the pumps so as to receive the flux near the pump or inside the base have not been entirely successful. For example, flux conduits in which inert gas and particulate flux are injected through an inner passageway of the conduit having a passageway on the order of an inch or less in diameter are ineffective in that they routinely become clogged.
Pumps of the type that include a base have been designed with a refractory shaft sleeve that extends between the motor support plate and the base. The shaft rotates inside the sleeve. Gas has been added into the shaft sleeve as disclosed in U.S. Pat. No. 5,676,520, and displaced the molten metal therein. However, the longstanding problem of how to effectively introduce flux with a pump for pumping molten metal instead of the hand lancing process, remains unsolved.